Method for coating catalyst supports

ABSTRACT

A method for controlling the coating with alumina of ceramic monolithic catalyst supports on a production basis to achieve repeatability of coating utilizing a vacuum system to distribute a coating slurry of alumina over the interior surfaces of and purge the excess coating slurry from the support at the same time that plugged tubular passageways through the support are unplugged, comprising the steps of applying the coating slurry to the support which has at least about 100 axially aligned tubular passageways to the square inch and subjecting the support to a vacuum to draw the slurry through the passageways and remove plugging and excess slurry to form a coating of alumina on the passageway surfaces. The support is dried and calcined to fix the alumina coating on the passageway surfaces.

BACKGROUND OF THE INVENTION

The catalytic conversion of the noxious components in vehicular exhaustgases is in current use for overcoming air pollution. The catalysts forthe various forms of converters are, at this time, being manufacturedand supplied in two general forms, namely: (1) as catalyst coated rigidskeletal monoliths, honeycomb type of elements, where there are amultiplicity of longitudinal passageways in each unit in order toprovide a high surface area; and (2) as confined masses or beds ofcatalyst coated pellets which may be generally of spherical orcylindrical form with diameters and lengths of about 1/8 inch.

The present invention relates to ceramic monolithic catalyst support andmore particularly, to an improved method for treating the catalystsupport in a controlled manner to effect a high surface area coatingthereon which is reproducible between supports, using apparatus adaptedto mass production requirements. It is essential from the standpoint ofcosts and attainment of the desired level of catalyst performance in aproduction process of the type herein described to be able to closelycontrol the coating operation for repeatable results between succeedingsupports, in order to minimize the amount of coating applied, especiallywhere the catalytically active material, e.g., platinum, palladium,rhodium, is codeposited with the high surface area material.

The rigid monolithic, honeycomb structures are typically made fromceramics which comprise refractory crystalline materials such assillimanite, magnesium silicates, zircon, petalite, spodumene,cordierite, aluminosilicates, mullite, or combinations thereof, etc.,cordierite being preferred because of the generally lower coefficient ofthermal expansion achievable, as shown in U.S. Pat. No. 3,954,672 toSomers et al. While such materials are generally considered to have aporous surface, it is generally advisable to provide a coating over thehoneycomb structure, e.g., active alumina, to achieve a high surfacearea for distribution of the catalytically active component. Thesemonolithic, substantially catalytically-inactive crystalline supportmembers have been described in prior art patents, as for example inKeith et al U.S. Pat. No. 3,565,830, and the British Pat. No. 931,096and its Japanese Pat. No. 292,558, such that it is not deemed necessaryto describe them in detail herein.

Typically, and by way of example only, the catalytic component willcomprise one or more of the noble and base metals and metal oxides ofGroups IB, VB, VIB, VIIB and VIII of the Periodic Table, particularlycopper, vanadium, chromium, manganese, iron, cobalt, nickel, platinum,palladium, rhodium and ruthenium, with a component being used singly orin combination with one or more of other active components.

While methods and apparatus are known in the art for coating a monolithsupport with a highly porous, fine grained, high surface area,refractory coating e.g., gamma alumina, the methods have either beensuch as to not lend themselves to mass production requirements or theapparatus has been costly and the process complex. The identified U.S.patent to Keith discloses the immersion of the monolith in the slurrywith agitation to coat the passageways fully, followed by shaking andgentle blowing with air to remove excess coating slurry and open theplugged passageways. Such technique is both time consuming and uncertainin its results and blow-back of slurry is not uncommon. The U.S. Patentto Hoyer et al U.S. Pat. No. 4,039,482 discloses a method for coatingwhereby the monolith is encapsulated in a sealed chamber in which it issuccessively subjected to vacuum to de-gas the pores of the structure,followed by contact with a flowing stream of the coating slurry whichflow is cut-off and, with the support submerged completely in the slurryin the chamber, pressure is applied to the slurry to force it into thesupport pores, this being followed by gravity draining and theapplication of air under pressure in the chamber to blow-down the excessslurry and unplug the passageways. A still further method for coating isdisclosed in U.S. Pat. No. 3,873,350 to Dwyer et al comprising the stepsof heating the support, immersing the support in the coating slurry,removing the coated support and draining excess slurry while shaking thesupport, and rotating the support about a substantially horizontal axiswhile blowing air through the passageways. U.S. Pat. No. 2,867,544 toHall, Jr. discloses a method for coating the inner wall surface of orfilling small diameter glass tubes wherein the tubes are first heatedfor obtaining adherence to and a continuous coating of the wall surfaceby the coating material, each tube being mounted between a pair ofaxially aligned holding members, the bottom members being connected tothe coating material source, the top member being connected to a vacuumsource which acts to draw the coating material up into the tube, theflow being interrupted by opening the bottom member to air.

SUMMARY OF THE INVENTION

In accordance with our method, a coating slurry of alumina is applied toa monolithic support having at least about 100 axially aligned tubularpassageways to the square inch extending from one end of the support tothe other and the support is then subjected to vacuum pressure to drawthe slurry through the passageways and remove plugging and excessslurry, the coating being repeatable between succeeding supports.

It is thus an object of our invention to provide a coating method whichutilizes subatmospheric pressure to purge the excess coating slurry fromthe surfaces of a monolith support having a large number of axiallyaligned tubular passageways while at the same time unplugging anyblocked passageways in the support.

It is another object of our invention to apply purging subatmosphericpressure in at least two stages in order to increase the through-put andenable control of the coating operation to assure uniformity andreproducibility of the coating.

It is a further object of our invention to provide a vacuum fixture ofrelatively simple design having means for subjecting one end of thesupport to vacuum and the other end to air of at least atmosphericpressure.

BRIEF DESCRIPTION OF THE INVENTION

These and other objects of our invention will be apparent from thefollowing description and the drawings in which

FIG. 1 shows a cross-sectional-elevational view of a coating and/orpurging station in a simplified system for coating monolith supports.

FIG. 2 shows a perspective view of a preferred system in which thecoating slurry application and purging are accomplished in a pluralityof coating-purging fixtures.

FIG. 3 shows a cross-sectional-elevational view of the coating andpurging fixture of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a purge tank 1 having an inlet oropening 3 on its top surface, a vacuum gage 5 to indicate the level ofsubatmospheric pressure in the tank, and an outlet conduit 7 which isconnected at a remote end, not shown, to a source of vacuum such as anexhaust pump or centrifugal blower having the capacity for maintaining adesired subatmospheric pressure level as described hereinafter ingreater detail. A support or holder member 9 is provided at the inlet 3to support in the opening 3 a ceramic monolithic support 11 having aplurality of passages extending from end-to-end thereof, the shape ofthe support being cylindrical, eliptical or of any other desiredconfiguration. As shown, the member 9 is a perforated support, themonolith 11 being positioned on the member 9 on one of its ends so as toplace the monolith passages in the fluid flow path through tank 1. Itshould be understood that the support or holder may take other formssuch as a mechanical clamping holder or other suitable means forsuspending the monolith 11 in the fluid flow path through the opening 3.Also provided within purge tank 1 is a baffle member 13 interposedbetween the inlet 3 and the outlet 7 in order to reverse the fluid flowpath and separate any entrained coating slurry from the air being drawninto tank 1 through the monolith support 11. Separated slurry iscollected in the bottom of tank 1 for recycling to the coating slurrysupply through valved drain 15. Arrows 17 indicate the air stream pulledthrough the monolith support and the purge tank by the high capacitypump in the outlet conduit 7. Droplets 18 represent the coating slurrybeing drawn through the monolith for collection in the bottom of tank 1on separation from the purging air stream 17. Flow lines 18' indicatethe coating slurry being flowed over the monolith support 11 wherecoating and purging are to be accomplished in the same station, 19'indicating a slurry charge holder. It should be understood that coatingmay be accomplished in an earlier station by either dipping the supportin the coating slurry or by flowing the slurry over the support surfacesin such earlier station. Also shown in FIG. 1 is a collar 19 adapted tobe positioned around the inlet 3 and the monolith support therein. Whenused, the collar 19 is spaced apart from the surface of the support 11to an extent allowing the air stream 17 to also flow over the outersurface and draw off excess coating slurry where the support has beendip coated.

In operating a system such as described, the monolith supports 11 wouldbe loaded continuously on a conveyor mechanism which would move themthrough the various stations for coating, purging, drying and calciningfor attaining a monolithic catalyst support having a repeatably uniformhigh surface area coating in the required amount for retention of thecatalytically active material in the minimum amount for the requiredcatalytic conversion.

In this regard it should be noted that a coating operation which doesnot produce coated supports with controlled amounts of coating, andtherefore catalytically active material, between successive supports,requires the use of maximum amounts of coating and catalytically activematerial to assure that there will be sufficient activity with eachsupport to carry on the desired conversion. Under such conditions manysupports have more than the required amount of catalyst and coating.

The conveyor may be either of the generally linear type or of therotating table type, this forming no part of our invention though weprefer the linear type for greater flexibility. Also, as would beobvious to those skilled in the art, the coating slurry may contain, inaddition to the suspended high surface area solids such as gammaalumina, catalytically active materials, e.g., platinum and palladium,in the form of water soluble salts, e.g, chloroplatinic acid andpalladium chloride. The amount of such materials required may be readilycalculated on the basis of the amount of coating slurry made-up and theweight of high surface area material left on the monolith after purging,drying and calcining. Such codeposition of the high surface areamaterial and the catalyst materials is preferred for simplicity andeconomy as well as control of processing.

As indicated, since the coating slurry is viscous, it tends to beretained in the passages of the monolith 11. The purge operation of ourinvention is intended to remove the excess slurry from the tubularpassageways and leave a uniform coating of the high surface area aluminaand catalyst material on the walls of the honeycomb structure. It isnecessary that the purge operation provide a uniform coating the amountof which, for the same size monolith support with the same slurry, issubstantially the same for each support passed through the coating andpurging operations. Further, since various sizes of support may bepassed through the system, the purging operation must be readilyadjustable to achieve the desired coating. Monolith supports of the typeherein discussed have at least about 100 axially aligned tubularpassageways to the square inch.

We have found that a high volume, low vacuum pressure pump is necessaryfor the desired results to be achieved. More particularly, we have foundthat a centrifugal blower rated at 1500 SCFM at a static pressure of 16inches of water is effective, with spare capacity for larger pieces, foraccomplishing the desired purging on monolith supports of 5.6 inchesdiameter by 7 inches long having square longitudinal passagewaysmeasuring 0.065 inches on a side with a wall thickness of 0.010 inches,there being 178 passageways to the square inch.

In operation, the coating slurry is applied to the monolith, either bydip coating or by applying a coating charge to the upper end of thesupport, and the blower is started with the support positioned in theopening 3. The vacuum is effective in each unplugged passageway of thesupport to draw the slurry over the wall surfaces, the air flow servingto wipe excess slurry from the walls. Due to the high volume capacity ofthe blower, the remaining plugged cells are also subjected to thesubatmospheric pressure in the tank 1 and the high volume capacity ofthe vacuum pump and are unplugged, excess slurry being collected in thebottom of the tank. The amount of slurry left on the monolith iscontrolled by the purge time and the vacuum pressure, at least about 30seconds total time at a static pressure of from about 5 up to about 16inches water being satisfactory. It is obvious that these factors may bereadily selected and adjusted based on the equipment available, coatingrequirements, and the sizing of the monolith support, it being onlynecessary that the subatmospheric pressure level be sufficiently low andthe volume capacity of the purge system sufficiently high to enableunplugging of passageways though even more than half of the tubularchannels in the support are unplugged. We have also found it to beadvantageous after the support has been purged from one end, to invertthe support and continue the purge from the opposite end. This has beenfound to improve the uniformity of coating distribution on thepassageway walls.

Having reference to FIG. 2, there is shown a perspective view of aproduction line of the preferred type for coating monolith supports inaccordance with our invention. In this embodiment, the monolith supports20 are shown being passed along a linear conveyor system through aseries of stations to the point where the coated monolith support ispacked in bins for either subsequent assembly in a catalytic converteror for impregnation with the catalytically active materials whereco-impregnation with the high surface area alumina slurry was notaccomplished.

More particularly, the monolith supports 20 from the extruding andcalcining operations are loaded onto a conveyer for movement to a weighstation 22 where the initial weight of each support is taken andrecorded for the purpose of coating control, each part being marked foridentification. The support then moves to the coating and purgingstation 24 where the support is positioned, by any suitable means suchas a movable clamp or calipers which comes in to grip the part and moveit into the desired position, in vertical alignment between a chargetube connected to a slurry tank 26 above the top end of support 20 andthe inlet 3 to the purge tank 1 below the bottom end of the support. Theclamp holding the support then cooperates with a conduit connected toinlet 3 to enable the establishment of either a sealed or an opensupporting connection between the conduit and the bottom end of themonolith support. Where a sealed connection is desired, it isestablished preferably about the outer peripheral surface or edge of thesupport 20 using a resilient sealing ring to minimize breaking stress.Alternatively, but not preferred, the seal may be established on the endsurface of the support radially inward from but closely adjacent to theperiphery, the outermost passageways being blocked. A preferred form ofconstruction of such sealing mechanism is shown in FIG. 3 and isdescribed in greater detail hereinafter. A similar sealing arrangementis provided at the top end of the monolith support with the feed tubefrom the slurry tank 26.

The coating and purging operation comprises releasing a measured amount,approximately one liter for the cylindrical parts previously described,of, preferably, catalyzed slurry from tank 26 into a tube having asealed connection with the top end of the monolith support as previouslydescribed. The tank 26 is then closed off from the tube which is open toatmosphere at a point above the surface of the charge of coating slurryand the monolith support is subjected to the subatmospheric pressure intank 1 by the opening of dampers or valves in the conduit 7, or at anyother suitable position in the air flow stream, such as at the inlet 3.The vacuum pressure is then effective on the monolith to draw the slurrythrough the passageways of the support. As a preferred example, we havefound that a total of at least about 30 seconds is sufficient time toremove the excess slurry and coat uniformly and repeatably the monolithspreviously described when using a centrifugal blower giving a staticpressure of about 6 inches of water as described.

It should be understood that the various actions into and within thecoating and purging station 24 are timed and sequenced as desired. Byway of example, it is preferred that the monolith support be subjectedto the subatmospheric pressure in tank 1 a short time, less than aboutone second, prior to the release of slurry to the support in order thatany leakage between the seal at the upper end of the support 20 be ofair into the support passageways to prevent loss of slurry to the outersurface of the support. Also, the sequencing may be timed to break theseal at the upper end of the support 20 after drawing the coating slurrycharge, this coating taking a period of about 5 seconds out of a totalof 15 seconds in the preferred example given, through the tubularpassageways, to supplement the air being drawn therethrough from theopening in the feed tube previously described.

Similarly, the through-put on the equipment may be increased by reducingthe time the support 20 remains in the coating-purging fixture 30 andmoving each support ahead to one or more additional purging fixtures 30'which are identical to the coating-purging fixture 30, includingconnection to a purge tank 1, except that the slurry tank 26 andconnection thereto is omitted. As shown in FIG. 2, we prefer themultiple purge fixture system and show the use of a first purge fixture30' connected to a first purge tank 1 together with the coating andpurging fixture 30. A second pair of purge fixtures 30' are shownconnected to a second purge tank 1'. Turnover means 32 is providedbetween the two pairs of fixtures to turn the monolith supportend-for-end in order to achieve more uniform coating of the passagewaysurfaces. Such turnover fixture may be of any design well known in theart. In the arrangement described, the monolith support 20 is residentin each fixture for a period of 15 seconds, thus producing a coatedsupport every 15 seconds.

The coated and purged monolith is then moved to a monolith supportrotating machine 34 where the supports are rotated at a rate of about 4RPM for a period of about 2 to 6 minutes, preferably about 4 minutes.This is an optional step in the processing of the monolith support butis preferred in our system since the rotation appears to prevent theslurry from sagging and improve distribution on the support. As shown,each part is automatically loaded into a rotatable holder on wheel 36 bya pusher device 38, similar mechanization being provided on the oppositeside to unload the support from the wheel. Alternate rotating systemsmay be readily devised by those skilled in the art, e.g., a conveyersystem in which each support is held on a rotatable spindle withsprocket at one end, separate chain means being used to rotate thesprocket and spindle, and such systems form no part of our invention.The support is then passed through a dryer-calciner oven 40 in which thefree water in the support is first dried in a flowing stream of air atabout 200° F. to an amount of about 0.5% by weight. We have found thatdrying may be conveniently accomplished in a dielectric oven over aperiod of about two minutes. The support is then calcined at atemperature of about 800° F. to remove combined water, this over aperiod of about 4 minutes. The removal of water prevents catalystmigration via water transport thus keeping the catalyst on the surfaceof the support. The part is then cooled and conveyed to a second scale42 where it is weighed, recorded and coating weight determined forcontrol purposes. After visual inspection for plugged passages and chipsand the like, acceptable supports are packed for assembly in thecatalytic converter or for impregnation with catalytically activematerial where co-impregnation in the slurry is not practiced. It shouldbe understood that the viscosity of the coating slurry may be adjustedas necessary to achieve the desired coating, a viscosity of from about60 to about 400 centipoises being used for the catalyzed slurrydescribed herein, though viscosities as high as about 3,000 centipoisesmay be used as described in assignee's copending application Ser. No.783,188 in the name of A. V. Somers, now abandoned the coating slurrybeing compounded as described in Ser. No. 783,188. In measuringviscosity, a #2 spindle was used at 60 rpm using an L.V.T. viscosimeter.Typical properties of catalyzed platinum-palladium-alumina slurry are

    ______________________________________                                        Range                  Preferred                                              ______________________________________                                        about 3.6-4.7                                                                              pH                                                               about 4                                                                       30-45        % solids                                                         about 37                                                                       60-3,000    viscosity cps.                                                   about 400                                                                     at least 100 surface area m.sup.2 /g                                          about 190                                                                     ratio of Pt:Pd % platinum -                                                                              about 0.9 of                                       = 5:2; weight              dry solids    about                                as desired for % palladium-                                                                              about 0.36 of 25                                   performance                dry solids    grams                                                                         ft.sup.3                             ______________________________________                                    

In Table I there is shown the results of tests coating a large number ofthe above described monolith supports to determine the effectiveness ofour method for flow coating monoliths of the kind describedhereinbefore. In this series the flow coating with vacuum was startedbefore the slurry charge was loaded at the top of the support.

                  TABLE I                                                         ______________________________________                                        Monolith Coating Test (Flow Coat)                                             Slurry  Static Pres-                                                                            Support,  Coating, Coating                                  Charge  sure inches                                                                             Dry Wt.   Dry Wt.  Pick-up                                  cc      H.sub.2 O/time                                                        gms.                                                                          gms.    %                                                                     ______________________________________                                        500     5.9/30/30 921.4     98.4     10.7                                     500     6.0/25/25 915.1     107.5    11.7                                     500     5.9/25/25 906.6     108.4    12.0                                     500     6.1/25/25 916.2     105.9    11.6                                     500     5.9/25/25 925.3     101.7    11.0                                     500     5.8/25/25 889.5     110.5    12.4                                     500     5.9/25/25 938.5     100.7    10.7                                     500     5.5/30/30 929.2     92.6     10.0                                     500     5.9/30/30 910.3     108.2    11.9                                     500     6.0/30/30 932.5     95.5     10.2                                     500     6.1/30/30 927.1     99.2     10.7                                     500     6.1/30/30 925.0     107.0    11.6                                     500     6.0/30/30 919.1     95.8     10.4                                     500     6.5/25/25 915.3     107.9    11.8                                     500     6.7/25/25 914.2     105.6    11.6                                     500     6.8/25/25 916.9     104.8    11.4                                     500     6.8/25/25 914.5     106.3    11.6                                     500     6.9/25/25 929.8     99.4     10.7                                     500     6.8/25/25 904.2     103.7    11.5                                     Average                     103.1 gms.                                                                             11.2%                                    ______________________________________                                    

In conducting these tests, a slurry charge of 500 cc was applied at theupper end of the support and a static pressure of from 5.5 to 6.9 inchesof water was drawn on the purge tank, each support being subjected tothis vacuum pressure for a period of 25 or 30 seconds on each end, i.e.,after being subjected to the vacuum for a period of time indicated, thesupport is reversed to place the upper end at the lower end position. Inthis manner we find we achieve a more uniform coating than when drawingthe vacuum from one end only. The slurry is drawn through the monolithsupport passageways during the first 5 seconds, approximately, and theremaining time is used to purge the excess slurry from their surfacesand to unplug those passageways which are blocked by slurry.

As can be seen from the data, about 84% of the pieces coated had theaverage coating weight of 103.1 grams ±5%, the remaining pieces beingwithin a 10% limit. Control of this character enables the use of a lowerover-all loading with the high surface area alumina and catalyticallyactive materials while still being assured of sufficient catalyticmaterials to achieve the desired level of activity and life for eachmonolith support coated.

Table II shows the results of tests coating a large number of theabove-described monolith supports using dip coating for applying coatingslurry to the monolith surfaces. As indicated, after dipping themonolith in the coating slurry and keeping it submerged therein for 30seconds, the supports were removed and cleared of excess slurry bydraining and application of blow-off air stream over the support for aperiod varying from 4 to 39 seconds. The parts were then subjected tovacuum pressure to purge excess slurry from and clear pluggedpassageways in the support. As noted, the supports were subjected topurge vacuum of 9.5 inches of water for a period of 30 seconds from eachend. The average coating weight is 99.4 and all parts but two are within±5% of the average.

                  TABLE II                                                        ______________________________________                                        Monolith Dip Coating Test                                                     Support,     Blow-off  Coating    Coating                                     Dry Wt. g.   time-sec. Dry Wt. g. Pick-up %                                   ______________________________________                                        1     943.0      18        101.3    10.7                                      2     930.8      39        96.0     10.3                                      3     936.4      24        101.9    10.9                                      4     934.6      34        97.5     10.4                                      5     944.0      29        101.6    10.8                                      6     944.4      36        99.1     10.5                                      7     944.9      28        99.8     10.6                                      8     946.0      31        100.3    10.6                                      9     943.6      28        97.8     10.4                                      10    949.1      29        100.0    10.5                                      11    941.9      27        95.6     10.1                                      12    941.8      24        99.3     10.5                                      13    932.1      21        100.8    10.8                                      14    928.2      21        98.6     10.6                                      15    938.0      20        100.8    10.7                                      16    941.7      19        97.9     10.4                                      17    944.1      16        98.0     10.4                                      18    934.0      16        101.8    10.9                                      19    945.4      18        96.1     10.2                                      20    945.1      14        98.5     10.4                                      21    944.7      12        96.5     10.2                                      22    929.0      14        99.8     10.7                                      23    935.1      9         100.0    10.7                                      24    943.5      6         96.5     10.2                                      25    949.4      4         100.6    10.6                                      26    940.7      7         94.9     10.1                                      27    944.1      5         87.1     9.2                                       28    927.8      6         122.1    13.1                                      29    942.8      5         103.1    11.0                                      30    950.1      10        100.0    10.6                                      Average            99.4 gms.  10.6%                                           ______________________________________                                    

As shown in FIG. 3, a suitable coating and purging fixture comprises apair of tubular connecting members 50 and 52 adapted to be brought incontact with the lower and upper ends of the monolith support when thesupport is brought within the treating station for coating and purging.The lower end 51 of lower connecting member 50 has an interconnectionwith the vacuum purge tank 1, shown as being telescopically sleevedwithin the inlet 3. Other interconnections such as described for member52 may also be used. The upper end 53 of upper connecting member 52 hasa sealed interconnection through a bellows member 54 with a slurrymetering member 56 connected to the slurry feed tank 26. As shown withrespect to lower connecting member 50, the various interconnections maybe made by telescoping pieces. Open type interconnections may be used inpracticing the method of our invention since the vacuum purge system hassufficient capacity to clear plugged passageways in the monolith supporteven though such passageways decrease and open passageways increaseduring the purge period of treatment. As shown in FIG. 3, the wall ofupper connecting member 52 has a plurality of vents 58 to assureavailability of sufficient air at least of atmospheric pressure toaccomplish the purging action through the monolith. The vents 58 arepositioned above the level of the coating slurry charge metered intoconnecting member 52, the vents serving to permit the vacuum to draw theslurry through the support. It is to be noted that in lieu of vents toatomsphere, the venting may be accomplished by recirculating the moistair from the outlet side of the vacuum pump, pressure of recirculatedair being controlled by suitable means forming no part of our invention.

The ends of connecting members 50 and 52 spaced from their correspondingends 51 and 53 are similarly designed to enable the members to form asealed connection with the upper end of the monolith support and anunsealed connection with the lower end of the support. Moreparticularly, each connecting member is provided with an annular plasticsealing ring 60 formed of a plastic material such as rigid polyurethanehaving resilience without being so soft as to fold down and block outerpassageways of the support when the seal is established in the mannerhereinafter described. A durometer reading of 70 has been foundacceptable with the polyurethane seals described. The inner peripheralwall surface of the ring 60 is formed with a conical face 61 openingoutwardly from the center thereof so as to enable convenient sealing ofmonolith supports of varying diameters. As shown, the sealing rings 60are retained on the ends of the connecting members 50 and 52 by clamprings 63 which are secured to the connecting members by screws 64 spacedaround the clamp rings. To achieve the unsealed connection with thelower end of the monolith support, a plurality of support tabs 66 areprovided on the sealing rings 60 so as to project radially inward toserve as supports for the end of the monolith support 20. These supporttabs are preferably thinner than the width of a passageway to preventblocking and may be formed as an integral part of the ring 60 or may beformed of stainless steel and inserted into receiving slots formed inthe ring 60. Stainless steel support tabs are preferred to reduce thecost of manufacture of the rings 60. Also, stainless steel is used toavoid interaction between the noble metal catalysts in the slurry andother metals which are lower in the Electromotive Series of Metals. Itis here to be noted that this concern for interaction requires that thematerials used in the coating and purging stations be either made ofnon-reacting materials such as teflon and polyurethane, or that metalsurfaces be coated with such materials to prevent interaction. It shouldalso be noted that the sealing ring 60 on the lower connecting member 50is provided with a radially extending drain groove 68 which cooperateswith an annular drip pan 70 clamped between the end of member 50 andsealing ring 60. Drip pan 70 serves to collect any dripping coatingslurry from the slurry tank 26 and from the described structural memberspositioned above the monolith support being treated.

As noted above, in our preferred design of the coating and purgingfixture 30, a slurry metering member 56 provides a measured amount ofslurry for application to the upper end of the monolith support held insealed contact with the conical face 61 of the sealing ring 60 on upperconnecting member 52. As shown in FIG. 3, the metering is accomplishedby providing a pair of spaced apart butterfly valves 57 and 57', thespace between the valve centers forming the metered volume of slurry. Inoperation, valve 57' is shut while valve 57 is opened to fill the valveblock with slurry. Upon closing valve 57 the metering member is preparedfor actuation upon positioning a monolith support between connectingmembers 50 and 52. When so positioned, the valve 57' is opened and themeasured volume of slurry is applied to the upper end of the support 20and coating and purging vacuum is applied, all in timed sequence asdesired and by means well known in the art. Alternative metering membersmay be used as is well known, i.e., a single timed valve may be operatedto secure the desired slurry charge.

In our preferred embodiment, the monolith support 20 is positioned inthe coating and purging fixture 30, in axial alignment betweenconnecting members 50 and 52 which are actuated to contact the ends ofthe support 20. As noted, in our preferred embodiment this establishes asealed connection with the upper end of the support 20 and an openconnection with the lower end of the support. It should be understoodthat the bottom end of the support 20 may also have a sealed connectionwith its sealing ring 60 or the top of the support 20 may have an openconnection as described. This latter open connection is not preferredsince coating slurry may then leak around onto the outer surface of thesupport 20, it being possible to minimize such leakage by drawing thevacuum through the monolith just prior to applying the slurry charge tothe monolith.

While alternative mechanizations are possible within the skill of theart, we prefer to use a pair of clamping arms or grips to pick-up themonolith support 20 from the moving belt by clamping the support betweenits ends, the support being rotated into position between connectingmembers 50 and 52 and there held by the arms. At least one of theconnecting members is then activated by any suitable means such as alinear or caliper type actuator to establish contact between theconnecting members and the ends of the support 20 as described. FIG. 3shows a fluid actuated piston-cylinder actuator 74 for establishingcontact. It should be understood that the timing and actuatingmechanisms form no part of our invention and may be selected as desiredby those skilled in the art.

As described, about the first 5 seconds of the vacuum treatment servesto draw the coating slurry through the support, the remaining period,about 10 seconds, serving to draw down excess slurry from the openpassageway surfaces and to start unplugging blocked passageways. Asdescribed and as shown in FIG. 3, the support 20 is then picked up by asecond pair of clamping arms 72 and is positioned in a purge fixture 30'which is identical with the first fixture 30 except for the omission ofthe bellows 54, the metering member 56, and the slurry feed tank 26. Thevacuum purge treatment is repeated in this fixture 30' for a period of15 seconds. The support is then again picked-up as before and rotatedend-for-end and positioned in a second purge fixture 30' for additionvacuum treatment and this may be repeated with vacuum applied at thesame rotated end. As noted above, the use of multiple treating fixturesenables a higher through put on the same production line.

Our invention in providing a simplified method and means for achievingrepeatable controlled coating of the many small size passageways in amonolith support has been described in the foregoing specification anddrawings. Additional advantages of our system to those describedhereinbefore will be apparent to those skilled in the art, suchadvantages including the economy and reliability resulting from use ofcoating and purging stations which are open to atmosphere andunencapsulated rather than using sealed chambers, and the fact thatapplicants vacuum system contains the coating slurry for ready reuse asopposed to a blow-off system which scatters the slurry. Alternative andequilavent steps and structure will occur to those skilled in the artand, to the extent covered by the attached claims are intended to bewithin the scope of our invention.

We claim:
 1. A method for coating with alumina porous ceramic monolithcatalyst supports having at least about 100 axially aligned tubularpassageways to the square inch extending from one end of the support tothe other so as to produce repeatable results on a production basis andutilizing vacuum pressure to continuously draw air through thepassageways to cause the coating slurry to flow over the porous ceramicwall surfaces of the tubular passageways of the monolith support,comprising the steps of applying the coating slurry containing highsurface area alumina in suspension to the support, subjecting one end ofthe support to a vacuum to draw the slurry through and form an aluminacoating on the passageways, continuing the application of vacuumpressure to unplug blocked passageways and to form a uniform coating andpurge excess coating slurry by the continuing drawing of air through theopen passageways, drying the support, and calcining the support to fixthe alumina coating on the passageway surfaces, the vacuum staticpressure on the support being from about 5 up to about 16 inches waterand being applied for a total period of at least about 30 seconds toachieve the desired coating and to remove plugging and excess slurryfrom the passageways even though the number of open passagewayscontinually increases during the period of vacuum treatment.
 2. A methodas in claim 1 wherein the coating slurry is applied by dipping thesupport in the coating slurry.
 3. A method as in claim 1 wherein thecoating slurry is applied by positioning the coating slurry on the upperend of the support, the lower end of the support being subjected tovacuum.
 4. A method for controlling the coating with alumina of porousceramic monolith catalyst supports having at least about 100 axiallyaligned passageways to the square inch extending from one end of thesupport to the other to achieve repeatable results on a production basisand utilizing vacuum pressure to form a uniform coating by thecontinuous drawing of air through the passageways to distribute thecoating slurry over the surfaces of and unplug blocked tubularpassageways of the monolith support, comprising the steps of positioningsaid support between a pair of connecting members with one member incontact with the upper end of said support and the other member incontact with the lower end of said support, the outer surface of saidsupport being unencapsulated and open to atmosphere, feeding saidcoating slurry to the connecting member at the upper end of saidsupport, subjecting the lower end of said support to a vacuum to drawthe slurry through the passageways, continuing the application of vacuumto unplug blocked passageways and to form a uniform coating and purgeexcess coating slurry by the continuing drawing of air through the openpassageways, removing the vacuum from said support, drying the support,and calcining the support, the vacuum static pressure on the supportbeing from about 5 up to about 16 inches water and being applied for atotal period of at least about 30 seconds to achieve the desired coatingand remove excess slurry from the open passageways and to unplug blockedpassageways despite the increasing number of open passageways during theperiod of vacuum treatment.
 5. A method for coating with alumina porousceramic monolith catalyst supports having at least about 100 axiallyaligned passageways to the square inch extending from end to end thereofto achieve repeatable results on a production basis and utilizing vacuumpressure to distribute the coating slurry over the surfaces of andunplug blocked tubular passageways of the monolith support, comprisingthe steps of positioning said support between a pair of connectingmembers with one member in contact with the upper end of said supportand the other member in contact with the lower end of said support,feeding said coating slurry to the connecting member at the upper end ofsaid support, subjecting the lower end of said support to a vacuum todraw the slurry through the passageways, continuing the application ofvacuum to unplug blocked passageways, removing the vacuum from saidsupport, drying the support, and calcining the support, the vacuumstatic pressure at the lower end of said support being from about 5 upto about 16 inches water and such pressure is applied for a total periodof at least about 30 seconds for coating the passageway surfaces, toremove excess slurry from the open passageways and to unplug blockedpassageways despite the increasing number of open passageways during theperiod of vacuum treatment, vacuum being applied first at one end ofsaid support followed by reversal by said support end-for-end withvacuum applied at the other end.